The alert for will run until 11am tomorrow morning.
A status yellow low temperature and ice warning will be in place from 6 o'clock for the midlands.
Met Eireann is forecasting temperatures to dip as low as minus four in places.
The alert for Leinster and Connacht will run until 11am tomorrow morning.
Liz Gavin is a forecaster with Met Eireann - she says there is also a change of ground frost: